Briquette of synthetic chromium ore



United States Patent BRIQUETTE OF SYNTHETIC CHROMIUM ORE Joseph C.Schumacher, Los Angeles, Calif., assignor to American Potash & ChemicalCorporation, a corporation of Delaware No Drawing. Application March 9,1951, Serial No. 214,850

1 Claim. (Cl. 75-3) This invention relates to a synthetic weatherproofchromium ore having a high chromium oxide content, and to methods formaking the same.

One object of the invention is to provide a synthetic weatherproofchromium ore of high chromium oxide. Another object is to provide asynthetic weatherproof chromium ore of high chromium content andrelatively low iron content from low grade natural chromite ore. Anotherobject is to provide synthetic chromium ore for use in metallurgicaloperations and in the stock-piling of chromate ore for subsequent use inmetallurgical operations. Still another object is to provide a processfor making synthetic weatherproof chromium ore of any desired chromiumcontent.

For use in metallurgical operations, and for use in stock-piling forsubsequent use in metallurgical processes, it is required that thechromium to iron content of the ore be in the ratio of 2.8 to 1, to 3.0to 1. Domestic chromium ores are available in which the chromium contentis acceptable, but in which the ratio of chromium to iron is about 2.5to 1, or lower.

I have discovered that a synthetic ore for use in blending to raise thechromium to iron ratio of a natural chromite ore to an acceptable valuemay be produced by chemically processing unacceptable grades of chromiumoxide to produce a product having a chromium oxide up to 98 percent,which may then be formed into weatherproof briquets or pellets by mixingwith a binder such as powdered calcium silicate glass and heating theformed mixture to the required temperature for binding the chromiumoxide.

My preferred process consists of first calcining low grade chromite withsodium carbonate in a rotary kiln at 900 to 1,200 degrees centigrade inan oxidizing atmosphere, thus producing soluble sodium chromate. Theproportion of sodium carbonate depends upon the nature and chromiumoxide content of the ore. One and onehalf pounds of sodium carbonate foreach pound of chromium oxide in the ore being treated is a generallysatisfactory amount. The soluble sodium chromate is then leached fromthe insoluble residue with water and the solution is neutralized or madeslightly acid with mineral acid, for example, sulphuric acid. Sufficientacid is added so that the silica and alumina which may have also beenextracted as sodium salts from the calcined material are precipitated.The insoluble precipitate is then separated from the soluble chromatesolution and, if desired, the alumina and silica may be recovered inuseful condition by suitable further processing.

The aqueous sodium chromate solution is then treated with sulphurdioxide gas preferably by means of a turbomixer, which treatment reducesthe chromium from the hexavalent to the tetra-, trior di-valent states,depending upon the completeness of the chemical reduction by thePatented Sept. 3, 1957 sulphur dioxide gas. In my preferred method, Ireduce to a mixture of tetra-valent and tri-valent chromium compounds.The following reactions are believed to take place:

The chromium is precipitated as chromium hydroxide Cr(OH)4 or Cr(OH)3 byneutralizing the reduced solution with a caustic alkali. Theprecipitated chromium hydroxides are then treated in washing thickenersto re move the soluble sodium compounds, after which the insolublechromium hydroxide compounds are filtered out, preferably on acontinuous rotary vacuum filter, and the filter cake is dried. I

The mother liquor and the wash water from the above operation may becausticized with lime to recover the sodium as sodium hydroxide, or theymay be discarded. The weak sodium hydroxide solution may be used inwhole or in part for neutralizing the chromium solution after thereduction with sulphur dioxide.

Other chemical processes for producing substantially pure chromiumhydroxides or oxides relatively free from iron compounds may be used.

The dried filter cake containing chromium hydroxides is then mixed witha binder such as powdered glass, or with lime and silica powders in theproper proportion to form glass. The amount of binder depends upon thedegree of binding as well as upon the fineness of both binder andchromium oxide, from 2 to 10 percent by weight being generallysatisfactory. The mixture is then formed into pellets or briquets inpelletizing or briquetting machines and these are calcined or heated tothe bonding temperature, for example, by passing them in cars through atunnel kiln where the temperature is held at 900 to 1,000 degreescentigrade. This heating operation produces dense, hard, water insolublepieces which have excellent weathering resisting qualities. Thesynthetic chromium ore may be mixed as required with the natural ore forstock-piling, or it may be used for immediate metallurgical operations,either alone or mixed with natural chromium ores.

The chemically prepared chromium hydroxides or oxides withoutbriquetting may be mixed as required with natural ore for immediatereduction to ferrochrome, in which form the chromium may be stock-piledfor subsequent use.

I claim:

A weatherproot briquette having high chromium oxide and low iron oxidecontent consisting essentially of a vitrified mixture of chemicallyprepared impure chromium oxides relatively free from iron oxide with avitrifiable silicate type bonding agent, the chromium oxide contentbeing above percent of weight.

References Cited in the file of this patent UNITED STATES PATENTS1,104,124 Mathesius July 21, 1914 1,121,226 Buddeus Dec. 15, 19141,422,703 Head July 11, 1922 r 1,586,590 Wild June 1, 1926 2,131,006Dean Sept. 20, 1938 2,197,146 Erasmus et a1. Apr. 16, 1940 2,243,785 UdyMay 27, 1941 2,416,550 Udy Feb. 25, 1947 2,416,551 Udy Feb. 25, 19472,480,184 Erasmus Aug. 30, 1949

